SQL practice set 1

Question 1

Table emp(id, name, dept, salary) has rows: Asha IT 60000, Ravi HR 40000, Neha IT 75000, Amit Sales 45000, Priya HR 52000, Karan IT NULL. What does SELECT COUNT(*) FROM emp WHERE dept = 'IT' return?

Accepted Answer

3

Question 2

Same emp table. What does SELECT COUNT(salary) FROM emp return?

Accepted Answer

5

Question 3

Same emp table. What does SELECT MAX(salary) FROM emp WHERE dept = 'HR' return?

Accepted Answer

52000

Question 4

Same emp table. How many rows does SELECT dept FROM emp GROUP BY dept HAVING COUNT(*) > 1 return?

Accepted Answer

2

Question 5

Which clause filters groups after GROUP BY?

Accepted Answer

HAVING

Question 6

Same emp table. What does SELECT name FROM emp WHERE salary IS NULL return?

Accepted Answer

Karan

Question 7

Which JOIN returns all rows from the left table, with matches from the right table (or NULLs)?

Accepted Answer

LEFT JOIN

Question 8

Which command removes all rows from a table but keeps its structure, and usually cannot be filtered with WHERE?

Accepted Answer

TRUNCATE

Question 9

Same emp table. What does SELECT name FROM emp ORDER BY salary DESC LIMIT 1 return?

Accepted Answer

Neha

Question 10

A PRIMARY KEY column must be:

Accepted Answer

Unique and not NULL

Question 11

Same emp table. What does SELECT ROUND(AVG(salary)) FROM emp WHERE dept = 'IT' return?

Accepted Answer

67500

Question 12

Which normal form removes repeating groups so that every column holds a single (atomic) value?

Accepted Answer

1NF

Question 13

What does SELECT DISTINCT dept FROM emp return for the same table?

Accepted Answer

IT, HR, Sales

Question 14

Which SQL keyword combines the results of two queries and removes duplicates?

Accepted Answer

UNION

Question 15

Same emp table. What does SELECT COUNT(*) FROM emp WHERE name LIKE 'A%' return?

Accepted Answer

2

SQL practice set 1

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